When auditory brain stem responses (ABRs and/or FFRs) are collected from three orthogonally placed electrode pairs and voltage is plotted in three-dimensional space, planar-curves are formed. The proposed studies will be directed initially toward defining the intranuclear origins of these planar-curves. Secondly, this recording technique will be employed to determine, at a first level, how simple and complex auditory stimuli are represented spatially in auditory brain stem nuclei in man and in the cat. Finally, this three-dimensional recording technique will be developed technically and tested, as a method for more efficiently deriving audiometric and neurologic information in human populations. To accomplish these goals, the specific source(s) of electrical activity contributing to the generation of the ABR or FFR from each nuclear subdivision of the cat's auditory brain stem will be defined, using three-dimensional planar-curve analysis in conjunction with selective biochemical ablation (micro-injections of kainic acid). A second approach will employ spatially controlled electrical stimulation of the auditory nerve array: to unequivocally relate cochlear place to three-dimensional map place, and to parametrically define the significance of temporal coincidence (or dispersion) relative to three-dimensionally recorded ABRs and FFRs. Results from these experimental approaches will, in part, provide the basis for further experiments, designed to define, at a first level, the "spatial representation" of given auditory stimuli within these nuclear subdivisions. Initial experiments will be concerned with mapping out the positions, in space, of planar-curves as a function of stimulus intensity; and of frequency. Other experiments will be directed toward determination of central spatial "maps" of perceptual qualities such as pitch, consonance and dissonance intervals, and critical band distance. These studies will employ simple and complex acoustic stimuli, as well as direct electrical stimulation of the auditory nerve array. A third set of experiments will be directed toward determining how maturation affects ABR planar-curve positions and patterns.